1. Field of the Invention
The present invention relates to a structure of an illumination push switch unit which is illuminated from an inner side, as in an electric apparatus.
2. Description of the Related Art
In recent years, various electric apparatuses, such as a television or a navigation system, an audio apparatus like CDs or cassettes, and an air conditioner, have been mounted in a vehicle. Further, various display units, such as characters or figures, are provided on operation surfaces of switch operation knobs for operating switches so as to clearly discriminate the switch operation knobs. Furthermore, in order to improve operability at night, each display unit is constructed such that it is a transmissive type and is illuminated through illumination from an inner side.
There has been known a structure for the illumination of such a switch operation knob (for example, see JP-A-2003-208835). According to the structure, light transmitting holes for illumination are formed in a substrate where predetermined circuits are formed such that they correspond to installation positions of switch operation knobs, LEDs each serving as light sources are mounted on a rear surface of the substrate, and operations surfaces of the switch operation knobs mounted on the surface of the substrate are constructed so as to be illuminated from the inner sides through the light transmitting holes.
The structure of the illumination push switch unit according to the related art is shown in FIGS. 7 to 9. FIG. 7 is a cross-sectional view of essential elements of the illumination push switch unit according to the related art, FIG. 8 is a cross-sectional view taken along the line VIII-VIII of FIG. 7, and FIG. 9 is a diagram illustrating each switch operation knob.
In FIGS. 7 to 9, a reference numeral 51 indicates a substrate where predetermined circuits are formed, and the substrate is disposed at the inner side of an operation panel 52. On the substrate 51, switches 53 composed of duct switches are mounted corresponding to various electric apparatuses mounted in a vehicle, and switch operation knobs 54 operating the switches 53 are mounted.
Each switch operation knob 54 is disposed such that its operation surface 54a is more exposed than an opening formed in the operation panel 52, and each switch 53 is operated by pressing operation. At this time, if a pressing force is released, the switch 53 returns to an initial state by a returning force of the switch 53.
Each switch operation knob 54 is formed so as to have a predetermined shape using an acrylic resin or polycarbonate resin having a light transmitting property. As shown in FIG. 9, in portions of the respective operation surfaces 54a, various transmissive display units 54b composed of characters or figures according to a switch function are formed to perform display through a coating material having a light transmitting property. In addition, in the other portions of the respective operation surfaces 54a, a coating material having a light shielding property is used.
In the substrate 51, light transmitting holes 51a are formed to correspond to mounting positions of the respective switch operation knobs 54, and LEDs 55 each serving as a light source for illumination are mounted on a rear surface of the substrate 51 corresponding to the respective light transmitting hole 51a. 
However, in the structure of the illumination push switch unit according to the related art, a barrier wall of the operation panel 52 disposed between the adjacent switch operation knobs 54, the adjacent side walls of the switch operation knobs 54, and the driving unit of the switch 53 are formed to a depth (length) which disrupts an optical path from a point of an extending line of the barrier wall toward light transmissive display units 54b of the adjacent switch operation knobs 54. For this reason, in the distribution illumination type in which a light-emitting unit is provided on the extending line of the barrier wall for illuminating the light transmissive display units 54b of the two adjacent switch operation knobs 54, it is required that each of the barrier wall of the operation panel (case) and the switch operation knob 54 is separately designed and manufactured. That is, there is a problem in that the operation panel (case) and the switch operation knob 54 can not be used for the distribution illumination type in which the light-emitting unit is provided on the extending line of the barrier wall.